1. Technical Field
The present invention relates generally to plug-type aircraft doors of the type adapted to swing through an arc approximating 180.degree. about a generally vertical axis between a fully closed position flush with the aircraft fuselage and a fully opened position wherein the door is disposed in a plane essentially parallel to the aircraft fuselage centerline and with the door's outer skin surface in face-to-face relation with the outer skin surface of the fuselage; and, more particularly, to a simple, effective, compact and improved cam operated counterbalance hinge assembly for assisting on-board flight attendants who are required to manually open and close such doors--doors which today often weigh in excess of 300 pounds--and who, in the performance of their duties, must lift the relatively heavy door upwardly while simultaneously pushing outwardly to open the door and, similarly, must again lift the door upwardly while simultaneously pulling the door towards a closed position. Such movement of the door, which presents difficult and awkward problems for on-board flight attendants, is necessitated because the hinge axis for such doors must be inwardly canted from true vertical so that the operating components of the hinge assembly can be mounted within the curved configuration of the fuselage body structure.
2. Background Art
Conventional commercial aircraft are commonly provided with a multiplicity of ingress and egress openings in the aircraft fuselage with suitable doors being provided for closure of such openings. The doors vary widely in terms of their construction and operation. Commonly, such doors are plug-type doors which are designed to fit into the ingress/egress openings when the doors are closed so as to form a substantially smooth, continuous, uninterrupted, exterior skin surface. When such doors are opened, they are pivoted about the axis of a first torque tube assembly mounted in the door and moved slightly inboard, at which point the doors are pivoted simultaneously about the axes of both the first door-mounted torque tube assembly and a second torque tube assembly mounted in the fuselage body structure and to which the door is hingedly connected, with the door moving outwardly through the ingress/egress opening and swinging through an arc approximating 180.degree. so that when fully opened, the door is entirely disposed outside of the aircraft fuselage, lying in a plane generally parallel to the aircraft centerline and with the door's outer skin surface essentially in face-to-face contact with the outer skin surface of the fuselage. In most instances today, such doors are manually operated by on-board flight attendants since most commercial aircraft carriers are reluctant to rely upon electrical actuating systems which are subject to electrical malfunction.
Moreover, as is well known to those skilled in the art, plug-type doors of the foregoing type, since they are required to conform in construction to the shape of the fuselage while providing access to the passenger compartment in the upper lobe of the aircraft, do not and cannot lie in a vertical plane either when fully closed or when fully opened; but, rather, they lie in a curvilinear plane having an inwardly canted chord line. As a consequence, the hinge assembly, including the fuselage mounted torque tube assembly, which must be entirely confined within the aircraft body structure, is inwardly canted from true vertical, often defining acute angles with the vertical of up to on the order of from 7.degree. to 10.degree., or slightly more. This, of course, means that when the door is opened and pivoted through an arc about the generally vertical, inwardly canted hinge axis, the door must be initially pushed outwardly while it simultaneously moves upwardly; and, once it has moved through approximately two thirds of its permissible pivotal movement, the door begins to move downwardly toward the outer skin surface of the aircraft fuselage. Conversely, when the door is closed, it must be pulled upwardly and away from the aircraft fuselage; and, when it has transitted approximately one-third of its arcuate movement about the inwardly canted hinge axis, the door begins to move downwardly towards and into the ingress/egress opening in the fuselage, thus closing the same. As commercial aircraft get larger and larger, such doors similarly become larger; and, consequently, the doors, together with door mounted actuating systems and the requisite emergency evacuation equipment carried thereby, have become considerably heavier, often weighing on the order of 300 pounds or more.
Thus, when an on-board flight attendant attempts to open the door manually, he or she is, in effect, required to push the relatively heavy door uphill during the intial portion of door-opening movement until such time that the door reaches the highpoint in its path of travel, at which point the weight of the door tends to swing it more rapidly downhill towards the fully open position. Even more difficult for the on-board flight attendant is the problem of closing the door which now must be pulled upwardly and away from the fuselage by the attendant, who is standing inside the aircraft, until the door again reaches its highpoint during pivotal movement about the inwardly canted hinge axis, at which point the weight of the door serves to cause it to move rapidly in a downward and inward direction towards the ingress/egress opening.
The foregoing problem tends to be uniquely applicable to aircraft where the door's hinge axis must lie within, and conform to, the chord of the curved fuselage body structure and, consequently, the hinge axis must define an acute angle with the vertical. Cabinet doors, housing doors, and similar type doors, on the other hand, do not face this type of problem because such doors are generally hinged about a truly vertical axis, thereby permitting movement of the door through the entire range of movement without having to lift the weight of the door in an upward direction during any portion of door opening or closure. Nevertheless, such doors have commonly included spring-type assist mechanisms, which have generally been provided to insure that the door is biased to at least one of a fully closed and/or a fully opened position. For example, Jordan, U.S. Pat. No. 1,028,571 and Bales et al, U.S. Pat. No. 1,831,800 each disclose arrangements wherein a door (a vehicle door in Jordan and a cabinet door in Bales et al) will generally be in a neutral unbiased position when it is halfway opened, but which moves in either direction from that neutral half opened position as a consequence of the provision of spring mechanisms which serve to bias the door from the neutral position towards both a fully opened and a fully closed position.
In Van Dillen, U.S. Pat. No. 2,028,424, a swinging door closing device is illustrated which employs a casing mounted mechanism biased by a pair of oppositely wound clock springs such that swinging movement of the door in one direction or the other tends to wind a respective one of the two clock springs to establish a restoring moment tending to bias the door towards the closed position.
Lundine, U.S. Pat. No. 2,557,749, discloses a cantilever-type spring which is mounted on a cabinet structure and which has its free end in engagement with the door. The arrangement is such that when the door is pivoted from a closed position, the spring is deflected to create a restoring moment for automatically closing the door; but, when the door is fully opened, the spring includes a detent-like arrangement for capturing the door edge and holding the door in its fully opened position.
Other patents of general interest illustrating spring-type biasing arrangements for non-aircraft doors are those found in, for example: Chamberlain, U.S. Pat. No. 2,587,287; MacDonald, U.S. Pat. No. 3,205,532; Murphy et al, U.S. Pat. No. 3,918,755; and, Wheeler et al, U.S. Pat. No. 3,115,685; the latter two patents illustrating combined spring-like camming arrangements and cam follower rollers for attaining the desired biasing motion to move a door towards a fully closed and/or a fully opened position.
Insofar as aircraft are concerned, counterbalance systems have also been known; and, they tend to vary widely dependent upon the type of door involved. In, for example, a plug-type door of the type adapted to move inwardly and upwardly along tracks disposed on the interior of the aircraft, it is common to provide a counterbalance system including cables and pulleys for minimizing the amount of exertion required to raise the heavy door upwardly along its tracks. Similarly, in Moses, U.S. Pat. No. 4,086,726, a counterbalance system is provided for an aircraft door which is intended to swing about a horizontal axis in an outward and downward direction for providing a ramp or steps permitting access to the aircraft.
In recent years, large commercial aircraft have faced problems similar to the problem faced and resolved by the present invention. In those types of door counterbalancing systems, the particular aircraft body structure has provided sufficient room to accommodate a plurality of coil springs--generally three such springs--coaxially and in generally end-to-end relation about the torque tube carried within the fuselage body structure. One of such coil springs was generally wound in a direction to permit biasing of the door in one direction during the initial portion of either door opening or closing movement, while the remaining two springs served to provide the biasing forces required during the initial portion of movement in the opposite direction. However, with present day aircraft where the doors are characterized by their large size and weight and wherein the aircraft aerodynamic contour is such that the hinge axis defines a significant acute angle, the weight of the doors has required the use of increased bearing supports, and supplemental snubber mechanisms, and the like, which provide retarding forces when the door is moving in either direction in a downward path so as to protect the door, the fuselage and the actuating mechanisms from damage due to sudden jars or shocks. Because of such mechanisms, and the constrained nature of the space within the fuselage body structure, it has been found that there simply isn't sufficient space for such coil springs in surrounding relationship to the body mounted torque tube.